Abstract
The fungicides TMTD (tetramethylthiuram disulphide) and ziram (zinc dimethyldithiocarbamate) decompose to carbon disulphide and dimethylamine in plain tinplate cans of acid foods. Trace levels of carbon disulphide cause pitting corrosion of the base steel of tinplate with little or no attack on the tin coating. Pitting corrosion differs from the usual form of attack in acid media in which tin is preferentially dissolved and steel is cathodically protected. Carbon disulphide induces pitting corrosion by reducing the hydrogen overvoltage of the tin coating so that cathodic protection of the steel becomes less effective. Carbon disulphide also accelerates anodic corrosion of steel. These effects are of sufficient size to cause inversion of the tin/steel couple potential. Dimethylamine increases hydrogen overpotential of tin slightly but has negligible effect on corrosion.
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